1. Field of the Invention
This invention relates to an insoluble and infusible substrate with a polyacene-type skeletal structure, an electrically conductive organic polymeric material obtained by doping the aforesaid substrate with a doping agent, and to an organic cell comprising the aforesaid material as an electrode and a solution in an aprotic organic solvent of a compound capable of forming dopant ions as an electrolytic solution.
2. Description of the Prior Art
Polymeric materials have excellent moldability, light weight and mass-producibility. It has been desired therefore in the electronics industry and many other industrial fields to produce electrically semiconductive or conductive organic polymeric materials by utilizing these excellent properties. It is especially desired to produce organic polymeric semiconductors or conductors which have an electrical conductivity in the range of semiconductors or conductors, possess the properties of n-type or p-type semiconductors as in inorganic semiconductors such as silicon and germanium, and can be applied to diodes, transistors, solar cells, etc. by utilizing their p-n junction.
Early organic polymeric semiconductors or conductors were limited in application because they were difficult to mold into films or sheets and did not have the properties of n-type or p-type extrinsic semiconductors. Recent advances in technology have resulted in the production of organic polymeric materials having the properties of n-type or p-type semiconductors, which have relatively good moldability and can be formed into molded articles, and of which electrical conductivity can be greatly increased by doping them with an electron donating dopant or an electron accepting dopant. Polyacetylene and polyphenylene are known as examples of such organic polymeric materials.
For example, "Gosei Kinzoku" Kagaku Zokan ("Synthetic Metals", Chemistry, special issue) No. 87, pages 15 to 28, 1980 discloses that by polymerizing acetylene, polyacetylene (having an electrical conductivity of 10.sup.-9 to 10.sup.-5 ohm.sup.-1 cm.sup.-1) in film form is directly obtained, and by doping it with an electron donating dopant or an electron accepting dopant, an n-type or p-type semiconductor having a greatly increased electrical conductivity can be obtained. Polyacetylene, however, has the defect of being susceptible to oxidation by oxygen. For example, when polyacetylene is left to stand in air, it gradually absorbs oxygen and increases in weight, and with it, turns black brown and finally pale yellow. The rapidity of this oxidation reaction depends upon the crystallinity of polyacetylene. For example, even powdery polyacetylene having a relatively good crystallinity prepared with a Ti(O-n-C.sub.4 H.sub.9).sub.4 -Al(C.sub.2 H.sub.5).sub.3 catalyst system changes in composition to (CHO.sub.0.18).sub.x and drastically decreases in electrical conductivity when it is left to stand in air at room temperature for 2,000 hours. Thus, despite its excellent electrical conductivity, polyacetylene has poor oxidation stability and finds little practical application.
Japanese Laid-Open Patent Publication No. 129443/1980 discloses that an n-type or p-type semiconductor having a greatly increased electrically conductivity can be produced by press-forming polyphenylene (an insulator having an electrical conductivity of about 10.sup.-12 ohm.sup.-1 cm.sup.-1) obtained by oxidative cationic polymerization of benzene, and doping the resulting molded articles of polyphenylene with an electron donating dopant or an electron accepting dopant. Unlike polyacetylene, polyphenylene has the advantage of possessing relatively good oxidation stability. Since, however, phenylene moieties are linked linearly by single bonds in polyphenylene, a conjugated system between carbon atoms is underdeveloped and there seems to be a limit in the level of its electrical conductivity which can be achieved by using a doping agent. Also, there seems to be a limit to the controllability of electrical properties by a doping agent. In fact, when polyphenylene is doped, for example, with halogen (an electron accepting dopant), the degree of its increase in electrical conductivity is smaller than that of polyacetylene doped with the same amount of halogen. Even when polyphenylene is doped with halogen in the largest dopable amount, its electrical conductivity does not increase beyond 10.sup.-7 ohm.sup.-1 cm.sup.-1 (see Example 5 of the above-cited Japanese patent document).
U.S. Pat. No. 4,375,427 discloses an electrically conductive organic polymeric composition comprising a polymer whose main chain is composed subsantially of (1) arylene units and (2) one or more chalcogen atoms or groups of such atoms interspersed between arylene units therein and at least one electron acceptor or donor dopant. The U.S. patent specification describes that this composition has a conductivity of at least 10.sup.-7 ohm.sup.-1 -cm.sup.-1.
In recent years, electronic devices and appliances have strikingly been reduced in size, thickness or weight, and with it, it has been increasingly desired to build electric cells in small size and thickness and light weight. Presently, silver oxide cells are in widespread use as small-sized electric cells of good performance. Thin dry cells or small-sized light-weight lithium cells of high performance have been developed and come into commercial acceptance. Since, however, they are primary cells, they cannot be used for long periods of time by repeated charging and discharging. On the other hand, nickel-cadmium cells have been used as secondary cells of high performance, but are still unsatisfactory in realizing small size, small thickness and light weight.
Lead storage cells have been used in various industrial fields as secondary cells of a large capacity. The greatest defect of these storage cells is their large weight. This is inevitable, however, since lead peroxide and lead are used as electrodes. In recent years, attempts have been made to decrease their sizes and improve their performance for use in electric automobiles, but have not resulted in practical cells. There has been a strong demand, however, for light-weight secondary cells of a large capacity as storage cells.
The cells now in commercial acceptance have their own advantages and disadvantages and are used selectively according to the desired uses.
To fill the present-day need for smaller sizes, smaller thicknesses and lighter weights, a cell has recently been developed which contains an electrode active substance obtained by doping a thin film of polyacetylene, an organic semiconductor, with an electron donating or accepting substance (see the specification of Japanese Laid-Open Patent Publication No. 136469/1981 corresponding to U.S. Pat. Nos. 4,321,114 and 4,442,187 and European Laid-Open Patent Publications Nos. 36118 and 124702). This cell is a secondary cell of high performance and could be rendered thinner and lighter. But it has the defect that the polyacetylene as an organic semicoductor is very unstable, and readily undergoes oxidation by oxygen in the air or degeneration by heat. This cell should therefore be produced in an atmosphere of an inert gas, and there is also a restriction in the molding of polyacetylene into a shape suitable as an electrode.
U.S. Pat. No. 4,472,489 discloses a polymeric electrode comprising a conjugated backbone polymer as electroactive material and a surface coating which is the product of reaction between a reduced conjugated backbone polymer and an organic compound such as sultones or sulfonates. The U.S. patent specification describes that the surface coating improves the stability of the electrode when the polymer is highly reduced during battery use.
The co-pending U.S. patent application Ser. No. 690,799 and European Patent Application No. 85100517.3 of the present applicants disclose a novel insoluble and infusible substrate with a polyacen-type skeletal structure which has a high surface area and exhibits excellent oxidation stability as well as excellent physical properties, an electrically conductive organic polymeric material composed of this substrate and a doping agent, and an organic cell comprising a positive electrode, a negative electrode and an electrolytic solution, at least one of the electrodes being composed of the above substrate and the above electrolytic solution being a solution in an aprotic organic solvent of a compound capable of forming ions which can dope the electrode by electrolysis. This secondary cell has a high electromotive voltage, a high charge efficiency and energy efficiency in charging and discharging, a high energy density and power density per unit weight, and a long service life and is maintenance-free and low in cost, but is still desired to be improved.